Human Self-domestication and Language Evolution: Focusing on Disorders
The objective of this doctoral thesis is to contribute to the current discussion of the origins of language in our species. Various hypotheses have been proposed to explain this conundrum, many of them with antithetical views. The framework adopted in this thesis, and the fundamental basis of the in...
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| Tipo de recurso: | tesis doctoral |
| Estado: | Versión publicada |
| Fecha de publicación: | 2022 |
| País: | España |
| Institución: | Universidad de Sevilla (US) |
| Repositorio: | idUS. Depósito de Investigación de la Universidad de Sevilla |
| OAI Identifier: | oai:idus.us.es:11441/136338 |
| Acceso en línea: | https://hdl.handle.net/11441/136338 |
| Access Level: | acceso abierto |
| Palabra clave: | Self-domestication language evolution neural crest Williams syndrome feralization language impairment Autism spectrum disorders social cognition social behavior neurobiology differentially expressed genes |
| Sumario: | The objective of this doctoral thesis is to contribute to the current discussion of the origins of language in our species. Various hypotheses have been proposed to explain this conundrum, many of them with antithetical views. The framework adopted in this thesis, and the fundamental basis of the investigation conducted therein, is the human self-domestication hypothesis. According to this hypothesis, specific characteristics of the human phenotype are a result, in part, of a process similar to that experienced by domesticated animals. The fact that many domesticated animals share common traits, known as the ‘domestication syndrome’ (DS) has led researchers to hypothesize that these cognitive, behavioral, and physical traits are the result of sexual selection of individuals with lower levels of aggression, in response to changes in a variety of environmental factors. One consequence of selfdomestication, according to this hypothesis, is the creation of a ‘cultural niche’, that is, a sociocultural environment that allows for the complexification of language via a cultural mechanism (Thomas and Kirby, 2018; Benítez-Burraco and Progovac, 2020). In this view, human language (particularly, languages used and spoken currently) can be seen as not only the product of biological factors, but also of advanced cultural aspects that characterise us as a species, which of course are also brought about by the same biological factors that shape language. This thesis is centered on the more variable aspects of human selfdomestication; since self-domestication is thought to be the result of physical changes related to control of aggression, it stands to reason that factors which favor prosocial behavior also heighten traits associated with self-domestication, and vice versa. Because more recently evolved traits are more vulnerable to ontogenetic damage, neurodevelopmental disorders prove to be key areas of study. A fundamental objective of the thesis is to determine the extent to which features of self-domestication are altered in disorders related to atypical or impaired socialization, and how this may contribute to the current understanding of language evolution. In order to do this, two main disorders were selected: Williams Syndrome (WS) and Autism Spectrum Disorders (ASD), which have traditionally been considered to represent opposite extremes when it comes to social behavior, with individuals with ASD exhibiting diminished traits of self-domestication (see Benítez-Burraco et al., 2016 for a discussion), and individuals with WS seemingly exhibiting exaggerated traits of self-domestication. The first article of this thesis (Niego and Benítez-Burraco, 2019) focuses on WS, with the main goal of discovering whether or not this assumption about exaggerated DS traits is true, and if the anecdotal evidence suggesting so can be substantiated with research. The research conducted for this article supports the fact that many traits of human self-domestication are indeed exaggerated in people with WS. In addition, various candidate genes for domestication in mammals are found to be significantly dysregulated in the blood of people with WS, suggesting that the WS deletion region may contain genes which are involved in the self-domesticated phenotype and that these genes affect the characteristic traits of WS. Once this characterization of ASD and WS as hypo- and hyper-domesticated conditions was established, the second and third articles of this thesis (Niego and Benítez- Burraco, 2020; Niego and Benítez-Burraco, 2021a) aimed to determine to what extent these conditions can be considered as opposite to each other in the sociocognitive realm. The fundamental reason for this was to determine if their opposite manifestations of the self-domestication syndrome affect the cognitive and social/behavioral phenotypes of both disorders. Article Two (Niego and Benítez-Burraco, 2020) concluded that ASD and WS cannot be considered to be opposites— neither in the phenotypical sense nor in the neurobiological sense. The third article (Niego and Benítez-Burraco, 2021a) extended this conclusion to the genetic realm, since a significant overlap was found between differentially expressed genes in the blood of ASD and WS. The aim was to investigate whether there are also quantitative differences at the phenotypic level which could be attributed to this genetic overlap. The results of both articles suggest that the case of ASD and WS is too complicated to explain these two disorders as opposite ends of a spectrum; both ASD and WS are not static conditions, but rather exist on a continuum, of which neurotypical people are also a part. The last two articles that make up the thesis, articles four and five (Niego and Benítez- Burraco, 2021b; Niego and Benítez- Burraco, 2021c) analyze feralization, a seemingly opposite process to domestication, and its impact on communicative capacity. Feralization is the process by which a domesticated animal returns to a wild-like environment. Understanding the extent to which feralization represents a genuine reversal of domestication and to what extent it can be seen as simply an adaptation to environment can aid in understanding the limits of the variation displayed in the selfdomesticated phenotype, both in neurotypical populations and in disorders. Article Four (Niego and Benítez-Burraco, 2021b) concluded that feralization does not in fact represent a complete reversal of domestication, but rather that certain physical, behavioral, and neurobiological traits revert to some extent. This investigation pointed to the fact that only a limited number of genes are involved in both feralization and domestication, and these genes can be considered to be promising candidates when it comes to explaining the sensitivity of self-domestication to environmental effects. Article Five (Niego and Benítez-Burraco, 2021c) sought to apply the conclusions derived from the previous article to humans, in particular, to clarify to what extent our characteristic sociocognitive traits (resulting from human self-domestication) are expected to revert as the result of genetic or environmental changes. In order to do this, Article Five made use of various lists of traits garnered from literature on feral animals with characteristics of individuals with ASD–a sociocognitive disorder known for its genetic origin– as well as individuals with Reactive Attachment Disorder (RAD) –a sociocognitive disorder known for its environmental origin. Given the principal objective of this thesis, special attention was paid to problems concerning language and communication in all of the groups which were studied. |
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